Children with specific language impairment (SLI) often show serious limitations in grammatical ability. A clearer understanding of the reasons for these limitations could lead to more accurate methods of diagnosis and more effective methods of treatment for these children. The purpose of the proposed project is to explore the possible bases of the serious grammatical limitations exhibited by children with SLI. To accomplish this general goal, the grammatical comprehension and production abilities of children with SLI will be examined across four languages, English, Italian, Finnish, and Hungarian. Data from these different languages will be used to assess the relative adequacy of three recent accounts of grammatical deficits in English-speaking children with SLI. Because the grammatical properties of Italian, Finnish, and Hungarian differ from those of English in critical ways, they offer a clearer view of the contribution of factors that are confounded in English, thereby facilitating interpretation of the data obtained from the English-speaking children with SLI. Inclusion of these other languages will also permit a determination of whether problems attributed to the grammatical details of tense and agreement are being compounded by problems with grammatical aspect. The experimental procedures are also designed to identify problems in sentence formulation that may exacerbate any difficulty attributable to limited grammatical knowledge. Finally, through careful selection of the grammatical details to be studied, it will be possible to determine whether children with SLI who speak African American English have serious difficulties in the same areas of grammar that have been found most fragile in mainstream American Englishspeaking children with SLI. Such a finding could lead to a uniform theory of how language impairment might develop and persist among children acquiring English.